Catt Sadler said it was her dream job. After 12 years at E! Entertainment, she was a co-host of two shows, “Daily Pop” during the day and the network’s flagship “E! News” at night.

But on Tuesday, she signed off for the last time because, she said, the company was paying her half as much as her male “E! News” co-host, Jason Kennedy.

Neither Ms. Sadler nor E! would disclose specific salary figures. Ms. Sadler said in an interview on Wednesday that in early 2017, a friend who is an executive at the network informed her of the disparity.

Once it came time to negotiate a new contract, she demanded to be paid comparably.

When the company refused, she decided she could not stay, she said.

“It’s heartbreaking in one sense, but I believe that you have to act in alignment with your beliefs,” Ms. Sadler said. “As much as I wanted to stay, I do know my worth, I do know the inner workings of the network, and I just wanted what was fair and reasonable.”

The network, which is owned by NBC, rejected the allegation that it paid Ms. Sadler less because she is a woman, saying in a statement that it “compensates employees fairly and appropriately based on their roles, regardless of gender.”

An E! spokeswoman said Ms. Sadler’s and Mr. Kennedy’s roles were not comparable.

In addition to co-hosting “E! News” five nights a week, Mr. Kennedy co-hosts “Live From the Red Carpet,” one of the network’s most lucrative programs, while Ms. Sadler was one of three hosts of “Daily Pop” and co-hosted “E! News” twice a week, the spokeswoman said. (“Live From the Red Carpet” airs before major awards shows like the Academy Awards and the Grammy Awards, not year-round.)

Ms. Sadler said she had taken on substantial new responsibilities when “Daily Pop” was introduced. For several months, she co-hosted both “Daily Pop” and “E! News” five days a week. She eventually cut back on her “E! News” duties because of the strain of doing both every day. Even after that, she said, she was hosting seven shows a week to Mr. Kennedy’s five.

“I inherited a lot more work and several more work hours, and I did all of that all year long without a single extra dime,” she said. “I did that in good faith because I’m a team player and I wanted both shows to succeed. I trusted that, come time to renegotiate, I would be compensated fairly for all of that work moving forward.”

Mr. Kennedy’s representatives did not respond to phone calls on Wednesday. Before Ms. Sadler’s final show, he tweeted that he would miss her but did not mention the pay issue.

Ms. Sadler said she hoped her decision would encourage other women to demand equal pay. As for her own future, she said she would love to host a show that would foster “discussions about this very topic.”

Acknowledging the support of Ms. Chastain, Ms. Munn and others, she said, “If these women celebrities and non-celebrities alike want to have these conversations on a huge scale for the world to watch and there can be some element of change that comes as a response to that, then that’s the kind of TV I would love to make.”